Subject: Re: [PATCH] perf/core: Fix account interrupt throttle
From:   Yang Jihong <yangjihong1@huawei.com>
To:     <peterz@infradead.org>, <mingo@redhat.com>, <acme@kernel.org>,
        <mark.rutland@arm.com>, <alexander.shishkin@linux.intel.com>,
        <jolsa@kernel.org>, <namhyung@kernel.org>,
        <linux-perf-users@vger.kernel.org>, <linux-kernel@vger.kernel.org>
References: <20230112033811.58924-1-yangjihong1@huawei.com>
 <93075101-43c8-b88e-8630-bce9e9a5f706@huawei.com>
Message-ID: <345704aa-46c5-5509-830d-8382d7b9c48d@huawei.com>
Date:   Mon, 6 Feb 2023 09:28:38 +0800
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Hello,

Ping again, please take time to review, thanks.


Thanks,
Yang

On 2023/1/28 9:28, Yang Jihong wrote:
> Hello,
> 
> PING
> 
> Thanks,
> Yang
> 
> On 2023/1/12 11:38, Yang Jihong wrote:
>> In literal sense of "max_samples_per_tick", if hwc->interrupts ==
>> max_samples_per_tick, it should not be throttled, therefore, the judgment
>> condition should be changed to "hwc->interrupts > max_samples_per_tick".
>>
>> In fact, this may cause the hardlockup to fail, The minimum value of
>> max_samples_per_tick may be 1, in this case, the return value of
>> __perf_event_account_interrupt function is 1.
>> As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
>> architecture as an example, see x86_pmu_handle_irq).
>>
>> Signed-off-by: Yang Jihong <yangjihong1@huawei.com>
>> ---
>>   kernel/events/core.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/kernel/events/core.c b/kernel/events/core.c
>> index d56328e5080e..ced98e028d86 100644
>> --- a/kernel/events/core.c
>> +++ b/kernel/events/core.c
>> @@ -9414,7 +9414,7 @@ __perf_event_account_interrupt(struct perf_event 
>> *event, int throttle)
>>       } else {
>>           hwc->interrupts++;
>>           if (unlikely(throttle
>> -                 && hwc->interrupts >= max_samples_per_tick)) {
>> +                 && hwc->interrupts > max_samples_per_tick)) {
>>               __this_cpu_inc(perf_throttled_count);
>>               tick_dep_set_cpu(smp_processor_id(), 
>> TICK_DEP_BIT_PERF_EVENTS);
>>               hwc->interrupts = MAX_INTERRUPTS;
>>
> 
> .